1. Field of the Invention
This invention relates to polyphase electrical generators and is applicable particularly to apparatus for generating power in the form of alternating electrical voltages between pairs of electrical output terminals, wherein each of said pairs of terminals may be isolated from others of said pairs and wherein the magnitudes and relative phases of the currents flowing between said pairs of output terminals, when loads are applied, are predeterminable.
2. Description of the Related Art
In the prior art two or more transformers may be driven from a single alternating current power source, which may itself be of a polyphase type, or else from a single phase source through phase shifting components such as capacitors. In either event it is possible for each pair of a plurality of pairs of output terminals to be linked by a plurality of winding turns connected in series, said turns being wound in appropriate number upon each of said transformer cores so that each turn makes a voltage contribution from the particular transformer core upon which it is wound. Between each of said pairs of terminals there will then exist a resultant voltage, formed by the vector addition of voltages from the said individual turns.
By choosing for each pair of terminals appropriate numbers of turns, wound upon one or more of said transformer corers, a voltage of any desired magnitude and phase can be obtained. However without the mechanical complication of movable coils, selection or variation of phase is available only in coarse steps corresponding to one winding turn.
This type of generator may well be complex and bulky, containing many junctions between individual windings: these are undesirable where a high degree of electrical isolation is called for. A particular example is diathermy used in electro-surgery, where the patient must be well protected from currents flowing to earth and also from any currents derived from low frequency power supplies.